By Brendan Sheppard and Steve Hargrave
Polyvinyl chloride (PVC) sheet piling (Figure 1) has been used for more than 25 years in bulkheads throughout the United States and beyond as a replacement for steel, concrete and timber materials due to the high corrosion resistance it offers in marine environments. More recently, barrier walls have been constructed for cutoff and containment applications using PVC sheet piles.
PVC sheet piling’s compatibility with hydrocarbons, solvents and common fuel additives like benzene, toluene, ethylbenzene, xylene and naphthalene [BTEX(N)] along with creosotes and other similar chemicals is of particular interest to engineers and their clients (OH DOH 2014). For these pollutants, PVC sheet piling can offer increased chemical cutoff and containment performance and design life, as well as reduced costs over conventional solutions. Because standard chemical resistance tables typically show these chemicals as “incompatible” or “not recommended” with PVC, there has been some hesitancy in the adoption of PVC sheet piling for chemical cutoff and containment applications. This article will review real-world levels for commonly contained chemicals and the resulting predicted permeation of the PVC sheet pilings used for their containment.
This article will also present cases studies in which PVC sheet piling has been used to cut off various types of groundwater contaminants, provide groundwater cutoff to construction areas, and serve as secondary and primary containment in dams. The article presents four case studies: a saltwater contamination cutoff wall in Bolsa Chica, Calif.; increasing storage for a fly ash pond near Brilliant, Ohio; remediation for a Superfund site in Michigan; and containment of groundwater and soil contamination in Corpus Christi, Texas. Key factors that engineers used in the decision-making process of specifying PVC sheet piles for these projects will also be highlighted.
Chemistry and permeation
Chemical compatibility tables are usually built from exposing the PVC to the “neat” or a highly concentrated form of the chemical approaching 100% purity. Indeed, at extremely high concentrations of toluene, for example, there can be deleterious effects on PVC ranging from degradation to swelling to softening. At lower concentrations, the degradation does not occur (Berens 1985).
In Berens’ investigation, “Prediction of Organic Chemical Permeation through PVC Pipe,” he concludes, “Softening and significant permeation of PVC pipe seems possible only in the presence of nearly undiluted solvents or swelling agents for PVC. At lower activities [concentrations], which still correspond to unusually high levels of environmental pollution, solvent transport follows ideal Fickian diffusion kinetics. . . . The calculated permeation rates are virtually zero for many centuries, indicating that rigid PVC pipe is an effective barrier against permeation of environmental pollutants” (1985).
Mao et al. (2011) validated and built on Berens’ research and developed a predictive model based on the behavior of toluene (the more aggressive PVC solvent component of BTEX) in National Institute of Standards and Technology (NIST) fuel. Equation 1 from “Microscopic Visualization Technique to Predict the Permeation of Organic Solvents through PVC Pipes in Water Distribution Systems” relates the swollen layer to the chemical’s concentration and time.
Applying this equation (Equation 1)
where:
Ls = swollen layer thickness (mm)
vf = volume fraction concentration
t = time (days)
to three common PVC sheet pile products results in the predictions for permeation shown in Figures 2a, 2b and 2c. At lower concentrations, the time to permeate a given thickness is on the order of centuries.
Additionally, in the Practical Handbook of Environmental Site Characterization and Ground-Water Monitoring (Nielsen 2005), Ranney and Parker concluded from their research with known PVC solvents (see List of known PVC solvents), many of which are on the U.S. Environmental Protection Agency’s (EPA) volatile organic compound (VOC) and semi-volatile organic compound (SVOC) target list, that at concentrations of 10% or less, there was no measurable degradation of PVC sample well casings:
List of known PVC solvents Nielsen 2005)
Hydrocarbons (aliphaticand aromatic)
- Benzene
- Gasoline (93 octane, unleaded)
- Hexane (85% N-hexane)
- Kerosene (K-1)
- Toluene
- o-Xylene
Chlorinated solvents (aliphatic and aromatic)
- Bromochloromethane
- Carbon tetrachloride
- Chlorobenzene
- Chloroform
- 1,2-Dichlorobenzene
- 1,2-Dichloroethane
- trans-1,2-Dichloroethylene
- Methylene chloride
- Tetrachloroethylene
- Trichloroethylene
Oxygen-containing compounds (either a ketone, alcohol, aldehyde
or ether)
- Acetone
- Benzaldehyde
- Benzyl alcohol
- Cyclohexanone
- Methyl alcohol
- Methyl ethyl ketone
- Tetrahydrofuran
Nitrogen-containing compounds
- N-Butylamine
- Diethylamine
- Dimethylformamide
- Nitrobenzene
Acids and bases
- Acetic acid (glacial)
- Hydrochloric acid (25% w/v)
- Sodium hydroxide (25% w/v)
Real-world containment levels
Many PVC sheet pile products have been installed in cutoff and containment barriers. These products have been exposed to chemicals ranging from acid mine runoff consisting of very acidic sulfur and iron compounds to polychlorinated biphenyls (PCB) to saltwater. However, the most commonly remediated contaminants are in the hydrocarbon family. These pollutants may consist of VOCs, solvents and fuels, including gasoline, which can contain up to 28% BTEX (Mao et al. 2011). Coal tar creosote also contains similar amounts of these compounds.
The vast majority of remediation projects experience contamination levels in the parts per million (ppm) or parts per billion (ppb), which are magnitudes lower than the ≤10% level cited in the Practical Handbook of Environmental Site Characterization and Ground-Water Monitoring. A survey of remediation projects of contaminated sites in the United States containing BTEX, or the individual components that make up BTEX, showed pretreatment contamination levels averaging 0.49%, with a maximum level of about 9% (EPA members 1995–2006).
Life expectancy of PVC with organic chemical containments
At contamination levels less than 40%, PVC sheet piling will perform well in chemical cutoff and containment applications with hydrocarbons, solvents and common fuel additives (Figure 3). Real-world contamination levels are most frequently in the ppm or ppb levels.
PVC sheet pile effectiveness in cutoff applications
The U.S. Army Corps of Engineers (USACE) recently published the Interim Poly Vinyl Chloride (PVC) Sheet Pile Guidance document, which provides guidance on the applications of PVC sheet piling as well as the important specification requirements. This document lists hydraulic cutoff barriers as an application for PVC sheet pile. In addition, the USACE recommends that all virgin PVC used shall have a minimum cell classification of 1-42443-33, in accordance with ASTM D4216, and that the manufacturer provide a certificate of analysis attesting to this along with the product warranty (USACE 2017).
The effectiveness of PVC sheet piling as a barrier can best be demonstrated by reviewing the real-world results from case studies. The following case studies were chosen primarily because of their age, postconstruction monitoring of the effectiveness and proven continued performance. Many other case studies are available. However, in many cases postconstruction monitoring data is not always readily available. Anecdotal evidence would suggest that the effectiveness of PVC sheet piles for cutoff applications is becoming more widely accepted by the engineering community as usage continues to increase.
Bolsa Chica
The Bolsa Chica Lowlands Restoration Project is the largest wetland restoration in Southern California history. The project created or restored more than 600 acres (243 ha) of marine and wetland habitat and was built as required mitigation for the expansion of the Ports of Long Beach and Los Angeles. Restoring the wetlands involved reconnecting the lowland to the influence of ocean tides and creating a full tidal basin and managed tidal areas. However, bringing the ocean tides back into the basin meant the possibility of saltwater contamination of neighboring groundwater. To prevent this, engineers specified that a 4,500-linear-foot (1,372-m) impermeable barrier wall be constructed to prevent saltwater migration. In September 2005, SG-325 PVC sheet piling was installed to a depth of 30 feet (9 m) to anchor the wall into a layer of impermeable clay. The wall installation was completed in just over one month using a steel mandrel and a fixed mast pile driving rig with a vibratory hammer. The full tidal basin was opened to the ocean on Aug. 24, 2006. Since the restoration of the wetlands, the seepage barrier has performed as intended. Figures 4a and 4b shows the aerial and ground-level wall alignment.
American Electric Power Cardinal Plant fly ash pond
Cardinal Fly Ash Reservoir No. 2 (FAR2) dam, located near Brilliant, Ohio, was originally constructed as a zoned-earth dam in 1985. In 1997, the dam was raised to a height of 237 feet (72 m) using roller-compacted concrete (RCC) in conjunction with a downstream earth fill. In 2011 the dam was raised again. The engineer specified a unique approach to raising the dam. A mechanically stabilized earth (MSE) wall system using geosynthetic reinforcement and reinforced full-height concrete panels formed the upstream and downstream faces to raise the dam 13 feet (4 m). For seepage containment, a cement-bentonite slurry wall was constructed, which penetrated into the existing clay core. A PVC sheet pile wall was then inserted 30 feet (9 m) through the slurry wall and extended up 8 to 13 feet (2.4 to 4 m) to the top of the raised dam in between the MSE reinforced zones. The use of PVC sheet pile allowed the cutoff wall to be a continuous element, eliminating the need for a horizontal joint, and was flexible enough to tolerate anticipated differential settlement. The benefits of the method chosen also included a reduced construction schedule to a single season, “Avoidance of weather sensitive materials, such as clay soils which could slow the construction schedule” (Rowland and Evans 2014), redundancy for seepage protection and reduced overall project cost. Figure 5 shows the PVC sheet pile wall installed and the MSE wall under construction.
Florida Gas Plant site
The Florida Gas Plant site located in Houghton County, Mich., is a former manufactured gas plant (MGP), which historically released coal tar waste into a drainage ditch that received seasonal flows of water into a nearby creek. Residential areas, a wetland and commercial businesses are adjacent to the site. At the Florida Gas Plant site, off-site migration of coal tar and dense and light nonaqueous phase liquids (D/LNAPLs) and organic chemicals posed a threat to groundwater, wetlands and nearby residents. Based on the results of a site investigation, engineers recommended installation of a cutoff wall. While traditional methods such as a slurry wall were initially considered for construction, engineers ultimately chose to install more than 600 linear feet (183 m) of SG-525 PVC sheet pile for containment. Beginning in August 2007, the PVC sheet piles were installed without any sealant in the locks to a depth of 17 feet (5 m) (Figure 6). The sheets were installed into soils with blow counts in excess of 50 using a steel mandrel system. Engineers checked the groundwater post-installation of the sheet pile system through the use of monitoring wells on a quarterly basis. The sheet pile wall was effective in containing the flow of contaminants from the site (EPA 2008).
Elementis, Texas
The groundwater and soils at this Corpus Christi, Texas, manufacturing plant became contaminated with high concentrations of benzene due to operations at El Paso Merchant Energy-Petroleum petroleum plant. Engineers were tasked with developing a cutoff wall solution that had a high resistance to degradation and minimized excavation and ground disturbance. The engineers working on the project specified SG-625 PVC sheet piling manufactured using coextrusion technology and hydrophilic sealant to be used in the interlocks to create an all but impermeable barrier. The SG-625 profile is 30-inches (76-cm) wide. This width minimizes the number of interlocks in the barrier wall as well as reduces the number of driving episodes for the contractor, thereby expediting the installation speed. The 32-foot (10-m) long sheet piles were installed into difficult soil conditions by a geotechnical contractor using a steel mandrel. The 1,000-linear-foot (305-m) wall was installed in November 2009 (Figure 7). Numerous monitoring wells were established around the site, and the groundwater is sampled on an ongoing basis to confirm the effectiveness of the barrier wall.
Summary and conclusions
PVC sheet piling and its compatibility with hydrocarbons, solvents and common fuel additives is often misunderstood in the context of real-world contamination levels. It has been demonstrated that concerns over compatibility using commonly available compatibility charts is not the right approach. PVC sheet piling has been used successfully for cutoff and containment applications on sites where organic containments are present.
Even in difficult soil conditions, PVC sheet piling can be installed effectively and efficiently using the right equipment and the right contractor. In many cases, the use of a mandrel allows contractors to install PVC sheet piles to depths of 30 feet (9 m) or more, and many contractors choose to use a fixed-mast pile driving rig to speed up the installation process. The 30-inch (76-cm) and 24-inch (61-cm) width of the PVC sheet piles used in these case studies was also a factor in the sheet pile products selected due to the speed of the installation and reduced number of interlocks. Engineers preferred the use of PVC sheet piling in applications involving contaminants due to the superior corrosion resistance and reduced ground disturbance. Engineers should be comfortable specifying PVC sheet piling in cutoff and containment applications because PVC sheet piling has been demonstrated to have real-world, long-term effectiveness.
Brendan Sheppard is the director of engineering of CMI based in Woodstock, Ga.
Steve Hargrave is the innovation and engineering director of CMI based in Woodstock, Ga.
All photographs courtesy of the authors unless otherwise noted.
References
Berens, A. R. (1985). “Prediction of organic chemical permeation through PVC pipe.” American Water Works Association Journal, 77(11), 57–65.
CMI Limited Co., Cutoff and Containment
Case Studies, CMI, cmilc.com/case-studies#Cut-
Off-Containment.
EPA (U.S. Environmental Protection Agency). (2008). Florida Gas Plant, EPA, response.epa.gov/site/site_profile.aspx?site_id=2752.
EPA members (Member Agencies of the Federal Remediation Technologies Roundtable). (1995–2006). Abstracts of remediation case studies, vols. 1–10 (Abstracts: EPA-542-R-95-001, EPA-542-R-97-010, EPA-542-R-98-010, EPA-542-R-00-006, EPA-542-R-01-008, EPA-542-R-02-006, EPA 542-R-03-011, EPA 542-R-04-012, EPA-542-R-05-021, EPA-542-R-06-002), National Service Center for Environmental Publications, Cincinnati, Ohio.
Mao, F., Gaunt, J. A., Cheng, J. A., and Ong, J. A. (2011). “Microscopic visualization technique to predict the permeation of organic solvents through PVC pipes in water distribution systems.” Journal of Environmental Engineering, Feb., 137–145.
Nielsen, D. M., ed. (2005). Practical handbook of environmental site characterization and ground-water monitoring, 2nd ed., CRC Press, Taylor & Francis Group, Boca Raton, Fla.
OH DOH (Ohio Department of Health, Bureau of Environmental Health). (2014). Health Assessment section, BTEX: Benzene, Toluene, Ethylbenzene, and Xylenes, Columbus, Ohio.
Rowland, M. G., and Evans, W. D. (2014). “Raising Cardinal dam using a unique double-sided MSE wall system.” Proc., Annual Conference, Association of State Dam Safety Officials, San Diego, Calif., 2, 773–784.
USACE (U.S. Army Corps of Engineers). (2017). “Interim poly vinyl chloride (PVC) sheet pile guidance,” Engineering and Construction Bulletin 2017-04.
World Health Organization. (2004). “Identity, physical/chemical properties, and analytical methods,” section 2. Concise International Chemical Assessment Document 62, Coal Tar Creosote, Geneva, Switzerland.